Today there is market demand for increasingly noiseless and compact projectors. Because it is desirable to maintain the light intensity despite the diminishing size of an image projector and because there do not appear to be imminent changes in relevant optical technology, the amount of heat generated by a projector will not appreciably change for the foreseeable future. To reduce to an acceptable level the heat generated by the lamp, a certain amount of heat must be removed from the projector per time unit. The integral product of volume flow and temperature increase across the openings in the projector chassis (i.e., the exit grill) is expressed as:∫ΔTin-out Cp p·vdA.The air flowing out of the projector should not exceed a temperature of 95° C. because this is the highest permissible temperature on the surface of a plastic exit grill.
A known problem with currently available projectors is that the air flowing out of the lamp reflector becomes very hot (200° C.-300° C.). To prevent it from heating the exit grill to more than 95° C., this hot air is mixed with cold air in a turbulent flow inside the projector. Since the projector size is to be as small as possible, such mixing needs to be done over very short distances. The device according to the invention permits efficient cooling of this kind and requires neither much space nor high air velocities. Low air velocities are desirable because they cause little energy loss in turbulence and hence little noise. To obtain minimum air velocities, all of the air exiting the exit grill should be close to the maximum temperature allowed. On the other hand, it is important that the cold airflow intended for mixing with the hot air remain along the length the projector chassis until the cold airflow reaches the exit grill, thereby preventing the surface from becoming uncomfortably hot to touch.
Another cooling problem that must be solved is keeping the temperature of the lamp tip (burner tip) from becoming excessively high. A certain airflow must, therefore, be conveyed past the lamp tip to prevent it from overheating and failing.